Operation: Saturate the wick of the wet bulb thermometer in clean water and whirl the sling psychrometer until the termperature stops dropping. Read the two thermometers. Place the wet bulb temperature over the dry bulb temperature scale on the slide rule. The arrow will then point directly to the accurate relative humidity.
Comes complete with a carrying case and slide rule. Range on thermometers is 20oF to 110oF.